1. Field of the Invention
The present invention relates to methods for the production phenyl-p-phenylenediamine (PPDA) and higher amines of structural formula (I) below from the starting material of structural formula(II) below. More particularly it relates to a method for preparing PPDA wherein aniline is oxidized in the presence of alkali metal pentacyano ferrate(II)complexes containing various water soluble ligands, such as ammonia, mono alkyl amine, dialkyl amines, and trialkyl amines, and utilizing oxygen or hydrogen peroxide as the oxidizing agents. The complex is then reduced by hydrogenation using suitable heterogeneous metal catalysts. ##STR1##
wherein n equals 2 to 5, and R.sub.1 and R.sub.2 are as set forth below ##STR2##
R.sub.1 and R.sub.2 may be the same or different, must be ortho or meta to the amino group, and may be hydrogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, halogen, cyano, carboxylate salts and amides of carboxylic acids or mixtures thereof.
The invention relates to the production of PPDA with the ability to recycle the transition-metal complex, high selectivity and yield. The conversion of aniline to N-phenyl-p-phenylenediamine is in the range of 40-85%. The yield of PPDA ranges from 91 to 97%. The method of this invention is also cost effective and produces no environmentally undesirable byproducts.
2. Background of the Related Art
The production of p-phenylenediamine and its derivatives is widespread and its uses are widely known. In U.S. Pat. Nos. 5,858,321 and 5,728,882 a complex made using ferrous chloride was used to prepare p-phenylenediamine. In U.S. Pat. No. 5,117,063, Stern et al., disclose various methods of preparing N-phenyl-p-phenylenediamine wherein aniline and nitrobenzene are reacted under specific conditions.
In other publications, the oxidative dimerization of aniline to produce N-phenyl-p-phenylenediamine is disclosed. British patent No. 1,400,767 and European patent 0-261096 utilize an alkali metal ferricyanide whereas European patent 0-272-238 utilizes a hypohalite oxidizing agent. None of these processes are very selective, nor do they give good conversions.
J. Bacon and R. N. Adams in J. Am. Chem. Soc., 90 p 6596 (1968) report the anodic oxidation of aniline to N-phenyl-p-quinonediimine but no conversions or yields are given. E. Herrington, in J. Chem. Soc. p 4683 (1958) reports the oxidative dimerization of aniline with disodium pentacyanoamminoferrate (III) to form a complex containing N-phenyl-p-phenylenediamine which is then reduced chemically with reducing agents such as hydrazine hydrate, sodium dithionate, sodium hydrogen sulfite and hydrogen sulfide. The use of the trisodium pentacyanoamminoferrate (II) complex and catalytic reduction with hydrogen of this invention distinguish over this publication and the differences result in a significantly improved process. The stoichiometry of the instant invention is much improved over Herrington since higher ratios of aniline to complex can be used in the process disclosed herein.
It is therefore an object of this invention to provide a method for the production of N-phenyl-p-phenylenediamine and related compounds. It is a further object of this invention to disclose a method for the production of such compounds via an aqueous process that allows the easy removal of unreacted aniline and subsequent separation of the reconstituted starting complex from the desired end product [formula (I)] after reduction giving a process which is commercially viable, involving both low cost and recyclability.
It is still a further object of this invention to provide a process that favors the p-phenylenediamine product, with both high yield and good selectivity. It is yet a further object of this invention to furnish a process with produces less waste and effluent streams. A still further objective is the production of phenylenediamine derivatives which may be used industrially as antidegradants made from the high purity products of the process of this invention.